Among caucasian infants there is a marked east to west trend in rates for the sudden infant death syndrom (SIDS). It has not been possible to explain this trend by differences in diagnostic procedures or by established risk factors such as mother's age, birthweight and family income acting as confounders. However, there are certain features of the epidemiology of SIDS which suggest a crucial etiological role for the environment; the east/west trend could therefore be of environmental origin. The strategy of this research project is based upon the observation that a significant proportion of the newborn's environment is controlled by its parents. The possibility that the environmental factor involved in the etiology of SIDS is parental in origin and geographically transferable is explored by an examination of SIDS rates among the offspring of couples who have migrated along the longitudinal axis within the United States. These rates will be compared to rates among the offspring of native-born parents and parents of mixed nativity. This research project is part of a larger inquiry aimed at understanding the role of the environment in the etiology of the Sudden Infant Death Syndrome. The study will be conducted on vital statistics of New York City, Oregon, Virginia, and North Carolina. These sites were selected because information on birthplaces of both parents is available on magnetic file, and the quality of cause-of-death certification is high. Instances of SIDS in infants less than one year of age and born in the years 1975-83 will be identified by ICD code number. Oregon and Virginia have state-wide medical examiner systems; North Carolina has a system in which there is shared authority between the county coroner and the county medical examiner; New York has a Chief Medical Examiner with deputies in each of the Boroughs. Data for North Carolina, Virginia and New York City will be combined in order to provide more reliable estimates of SIDS in the east. Information on risk factors that are potentially confounding will be obtained from birth certificate entries. Birth and death certificate information will be available on one consolidated computer file. This will enable the questions to be addressed by means of chi-square tests of significance and cohort logistic regression analyses.